Electromagnetic devices



July 15, 1969 E. PADDISON ET AL 3,456,219

ELECTROMAGNETIC DEVICES Filed Jan. 18. 1966 FIGZ INVENTORS ERIC PADDISONGORDON JOHN LALLY United States Patent Olfice Int. Cl. H01t 3/00 US.'Cl. 335-298 3 Claims ABSTRACT OF THE DISCLOSURE An electromagneticdevice defining a closed magnetic circuit includes a shell-typelaminated magnetic core having a centre limb carrying a winding andhaving a pair of pole pieces whose opposing surfaces are spaced apartfrom one another. The winding is energisable to cause the pole pieces toassume opposite polarities. A tapered elongate magnetic member isdisposed between the pole pieces with its major axis extendingtransversely of the center limb of the core to provide two air gaps oneon each side of the major axis of the member. The member is mounted onthe core and movable along its major axis between stop positions to varythe reluctance of the magnetic circuit. The opposing surfaces of thepole pieces and the member have the same shape and the same angle oftaper so that, for any position to which the member is moved, each airgap is of constant length over the whole of the opposing surface of therespective pole pieces.

This invention relates to electromagnetic devices, and particularlyrelates to means for varying the reluctance of a magnetic circuitdefined by such a device.

From one aspect, the present invention consists in an electromagneticdevice comprising a magnetic core defining a closed magnetic circuit andhaving opposing poles spaced apart from one another with an air gaptherebetween, and a magnetic member mounted in said gap and relativelymovable between the poles, the surfaces of the poles and/or the memberbeing so shaped that the mean spacing between opposing surfaces of thepole and member varies in response to said movement whereby to vary thereluctance of the magnetic circuit.

In accordance with this invention the magnetic reluctance of the deviceis varied without substantially altering the cross-sectional area of theflux path.

The invention is of particular utility in transactors employed inprotective relays in which the ratio of the secondary voltageto primarycurrent may be varied by the movement referred to above.

In order that the invention may be fully understood a device having alaminated magnetic core and adjustable reluctance will now be describedby way of example, with reference to an accompanying drawing in which:

FIG. 1 shows a cross-sectional view of the device hav ing a movablemember for adjusting the reluctance; and

FIG. 2 shows a circuit diagram of an adjustable transactor whosewindings are wound on the laminated magnetic core in FIG. 1.

Referring now to the drawing a winding 8, having input terminals 9, ismounted on a shell-type laminated core which has two magnetic polepieces 11 and 12 defining between them a tapered air gap of rectangularcross section. A- similarly tapered laminated member 13 is disposedtransversely in the air gap, the member being internally threaded andmounted on' an adjusting screw 14 which is in turn supported by limbs 15and 16 of the core. The member 13 has two non-magnetic stops 17 and 18arranged to prevent the member moving beyond desirable limits ofmovement; that is, beyond either side of 3,456,219 Patented July 15,1969 the air gap between the poles 11 and 12. A spring 19 between thelimb 15 and the stop 17 is efifective to urge the member 13 in adirection away from the head of the screw 14-to prevent undesirablemovement of this member, when magnetised for example, due to back-lash"in the adjusting screw threads.

A pointer 20.is arranged to be moved around a scale 21 in response tomovement of the member 13 and is held against the stop 18 by a spring22.

In operation, when the coil is energised, translational movement of themember 13 varies the length of the air gap and thereby the reluctance ofthe magnetic circuit, and the scale 21 may conveniently be calibrated sothat it can exhibit predetermined settings of inductance possessed bythe device.

It will be appreciated that the air gap may be anywhere within themagnetic circuit of the core and that the air gaps between the poles andthe member may be any shape in cross-section, e.g. rectangular orpart-annular, provided that the effective length of the air gap may beadjusted by limited relative movement between the member and the polepieces 11 and 12 without substantially altering the effectivecross-sectional area of the flux path between these two poles.Similarly, the magnetic core itself may be in any form defining acontinuous magnetic circuit having one or more air gaps, for example,the core may be shaped substantially as a ring or the letter C.

As an example, one application of the device of FIG- URE 1 is in theadjustable transactor of FIGURE 2 which includes a primary winding 23energisable from a current source 24 and a secondary winding 25connected to a load 26. The windings would be wound on the centre limbof the magnetic core 10 in a similar manner to that shown by the winding8 in FIGURE 1. The secondary ampere-turns are arranged to be smallcompared with the magnetising (primary) ampere-turns so that when theprimary winding 23- is energised a voltage output will be produced fromthe secondary winding 25 which is proportional to the current in theprimary winding 23 but approximately out of phase therewith. When thelength of the gap is adjusted by the means provided, the ratio betweenthe secondary volts and primary current may be varied. The scale maythen be calibrated in terms of this ratio or in terms of the primarycurrent for a specific output voltage.

What we claim as our invention and desire to secure by Letters Patentis:

1. An electromagnetic device comprising a magnetic core defining aclosed. magnetic circuit,

said core having pole pieces with opposing surfaces spaced apart fromone another,

a winding carried by the core and energisable to cause the pole piecesto assume opposite polarities,

a tapered elongate magnetic member mounted between the pole pieces withpart of the member'lying between the whole of said opposing surfaces ofthe pole pieces to define between said member and the pole piecestwo airgaps one on each side of the major axis of said member,

means for moving said member along its major axis to vary the length ofthe air gaps and thereby the reluctance of the magnetic circuit, and

limit stops on said member for confining the movement thereof so thatpart of said member always lies between the whole of said opposingsurfaces of the pole pieces,

the said opposing surfaces of the pole pieces and the opposing surfacesof the member having the same shape and the same angle of taper whereby,for any position to which the said member is moved by said means, eachair gap is of constant length over the whole of the opposing surface ofthe respective said ment is dependent on the relative position of saidpole piece. member and said pole pieces. 2. In a transactor, a deviceaccording to claim 1, in-

eluding a primary winding and a secondary winding References C mountedon said core, a current supply means for ener- 5 IT STATES PATENTSgizing the primary winding to induce a voltage into the 2 4 795 1/1954it g 3364434 XR secondary winding, the secondary ampere-turns being1076:2358 4/1937 I small compared with the primary ampere-turnssufiicient 32192 442, v 5/1965 warrington et a1: 317-36 to insure thatsaid'voltage is proportional to said primary 3,193,729 7 1965 Paddisoncurrent at any width of said air gap, the said movement 10 3 207 9 1 9 95 m- 5 of the member being effective to vary'the ratio between 3,278,87510/1966 McDonough 335 272 the secondary voltage and the primary current.3,325,660 6/1967 Boyer.

3. A device according to claim 1, including indicating means forindicating the position of said 15 BERNARD GILHEANY, Prlmal'y Examlnermember relative to said pole pieces, said indicating 11 M, MORGAN,Assistant E i Q means having a pivotally mounted element operativelyconnected to U.S. Cl. X.R.

said member so that the angular position of said ele- 336134

